1. Field of the Invention
The invention relates to a multilayer card, in particular credit card, bank card or ID card such as national ID document, driver's license or other identification document, which has a security element with relief structures which produce open and hidden representations, as well as a method for manufacturing the card.
2. Related Art
Cards which for different kinds of reasons represent an object of value, such as bank cards, credit cards or ID cards, must be protected against forgery. For securing such value cards against forgery, there are often employed security elements with security features in the form of relief structures, for example embossed holograms, the manufacturing of which requires a significant technological effort. One reason for the popularity of such security elements is that the optical effects yielded through the diffraction structures or refractive structures cannot be reproduced even by state-of-the-art copying machines, but can be rather simply checked by a viewer.
Mostly, the security elements having relief structures are adhesively bonded to an outer surface of the card. There are adhesive bonding techniques which make it possible for the security elements to be very durably fixed on the card surface, so that a non-destructive detaching of an adhesively bonded security element is nearly impossible. Security elements adhesively bonded to an outer surface of a card, however, upon the use of the card, are subject to heavy wear, and in particular in the case of frequently used cards or cards which are used for a very long time, such as ID cards, the relief structures suffer within a too short period of time due to abrasion and other mechanical loads in such a way that the optical effects are lost.
It was therefore attempted to embed security elements with relief structures in the interior of the cards, so that the security elements are protected from mechanical wear by card layers. However, a security element to be embedded between card layers is exposed to the effects of heat and pressure during the lamination process of the card layers, and the quality of the relief structures is impaired thereby so much that the optical effects can no longer serve as a security mark. To avoid a damage of the relief structures during the lamination process, it was proposed to expose the card areas, in which there is located a security element having relief structures, to less high temperatures and a lower pressure during the lamination. Such a method is described, for example, in EP 0 013 557 A2. Through the more careful treatment of the security element areas during the lamination, however, there is achieved only a slight improvement in terms of maintaining the quality of the relief structure, and this improvement is bought at the cost of a worse foil composite in the card areas treated more carefully, which has a negative effect on the visual recognizability of the security features of the security element, and, moreover, in the course of time can lead to a splitting of the card layers in this area.
However, special problems arise in the case of security elements which have relief structures with first and second picture elements, the first picture elements producing to the viewer first, so-called “open” picture information (representation) and the second picture elements producing to the viewer, using a suitable aid, second, so-called “hidden” picture information (representation). In the following, the first and second picture elements are also referred to as “open” and “hidden” picture elements. Upon viewing the security element, a viewer without aids can recognize only the open picture information (representation) which is produced by the interaction of the incident light with the open picture elements of the security element. But for reading out the hidden picture information of the security element, i.e. for recognizing the hidden representation, there are required specific aids. Security elements with relief structures, in particular diffraction structures, with open and hidden picture information have a very high degree of forgery-proofness. Here, one virtually has a security feature protecting an object against forgery (the open representation produced by the open picture elements), which security feature in turn is protected by an internal security feature (the hidden representation produced by the hidden picture elements) against forgery.
Security elements with a diffraction structure, which have first and second picture elements for producing open and hidden picture information, can be manufactured for example according to the methods described in WO 2005/038499 A2. With respect to security elements with first and second picture elements for producing open and hidden picture information as well as with respect to their manufacture, the disclosure of the WO 2005/038499 A2 is expressly made the subject matter of this application.
From WO 2005/038499 A2 it is known to emboss the first and second picture elements with suitable embossing heights as a relief structure in an embossable layer. From WO 2005/038499 A2 it is further known that in particular the relief structure of the second picture elements, which produce the hidden information (hidden image), is very sensitive to external influences, such as wear or crease. The sensitivity of the relief structures producing the hidden picture information is also due to the fact that these relief structures are normally extraordinarily fine so as to not impair the open picture elements of the security element and therefore not to diminish the open representation perceived by the viewer.
The normally extremely fine structures of hidden picture information, which can be characterized for example by first picture elements with an embossing depth lower than the embossing depth of the second picture elements, are not only extremely sensitive to mechanical stress such as abrasion or crease, but also to temperature loads. If security elements with diffraction structures with visible and hidden picture information are laminated into the layer composite of a card having several laminated layers, the picture elements producing the hidden representation are severely damaged or completely destroyed by the pressures and temperatures required for the lamination.
A decrease of the lamination pressure and the lamination temperature in the area of the security element, as described in EP 0 013 557, leads, as already explained, to a poorer foil composite in this area and impairs the visual recognizability of the security features of the security element, in particular the detectability of the hidden representation, insofar as this has not yet been destroyed despite the more careful treatment.
Doing without the lamination into the interior of the layer composite of a card does not solve the problem either. Security elements which are adhesively bonded substantially without pressure and temperature load to an outer surface of a card, offer less protection against forgery, since, in contrast to a laminated security element, they can possibly be removed. Furthermore, because of the lack of protection by a card foil, such security elements are exposed to increased wear, which may lead to the fact that the hidden picture information soon cannot be detected, i.e. made visible with aids, any longer.
So there is the problem that with the current methods of the prior art it is not possible to mount a security element with first and second picture elements, which produce open and hidden picture information, on a card such that it cannot be removed without damage, and the sensitive structures are neither damaged by the application method of the security element nor through extended use of the card and are well visible or well detectable. The seemingly insoluble dilemma is: for a high degree of forgery proofness, hidden picture information is desirable and the lamination of the security element into the card's layer structure is required. Under lamination conditions, the fine structures of the hidden picture information are regularly destroyed. On the other hand, particularly careful lamination conditions impair the visual recognizability or detectability of the security features and the composite strength of the security element in the layer structure of the card.
It is therefore the object of the present invention to provide a card with several layers laminated with each other and with a security element which a security feature on the basis of relief structures, in particular diffraction structures, with first, open and second, hidden picture elements, which produce a first, open and a second, hidden representation (picture information), which card has a high degree of forgery proofness.
It is furthermore the object of the present invention to provide such a card, wherein the security element has a high composite strength in the layer structure of the card.
It is further the object of the present invention to provide such a card, wherein there is guaranteed a good visual recognizability of the security features of the security element, and in particular a good detectability of the hidden picture information.
It is moreover the object of the present invention to provide a method for manufacturing such a card.